fix(frontends/lean/parser): bugfix AST export (#634)
fix(frontends/lean/parser): bugfix AST export (#634)

The node was being double finalized and resetting its id to the original
one before parsing the universe levels, resulting in the universes
getting discarded.

Fixes leanprover/mathport#36



leanprover-community/lean,leanprover-community/lean,leanprover-community/lean,leanprover-community/lean,leanprover-community/lean,leanprover-community/lean